The purpose is to characterize existing lines of cells and develop new lines of cells that in culture perform transepithelial transport of interest to the nephrologist. We are attempting to start new lines of cells beginning with primary culture from microdissected segments of the nephron. Cells of lines cultured from the toad urinary bladder transport sodium actively. The rate of transport is stimulated by aldosterone and by cyclic AMP. The latter stimulates permeability to urea but has no effect on permeability to water.